More than two dozen of null mutants of alpha-glycerol phosphate dehydrogenase have been identified in natural and gamma-induced or EMS-treated Drosophila populations. To understand the nature of gene mutation in alpha-Gdph locus, we have analyzed these null mutants by double immunodiffusions, rocket immunoelectrophoresis and two-dimensional electrophoresis. One out of nine mutants identified in Drosophoila natural populations was shown to be CRM-negative. One out of four mutants identified in gamma-irradiated Drosophila was shown to be CRM-positive. All the EMS-induced null mutants were shown to be CRM-negative.